, 2007); and oligodendrocytes (Mo and Zecevic, 2009). Although a plethora of dividing precursors has been identified in the developing primate VZ, molecular techniques initiated approximately a decade ago, including in vivo retroviral labeling and transgenic targeting, suggested that the rodent VZ contains a homogeneous population of RGCs. Rodent RGCs undergo self-renewal, generate

neurons directly, and give rise to the basal INPs in the SVZ (Noctor et al., 2004) expressing the transcription factor Tbr2 ( Englund et al., 2005). Hence, rodent RGCs essentially perform all of the roles required for neocortical growth (Tbr2+ SVZ progenitors are distinguished by their transient localization in the SVZ and association with capillaries ( Javaherian and Kriegstein, find more 2009 and Stubbs et al., 2009) prior to terminal division and migration to the cortical plate). However, this RGC-centric model has been modified by several studies using retroviral labeling, in utero electroporation, as well as other molecular methods such as cell sorting and time-lapse

imaging, which indicate that RGCs can be antigenically and functionally separated into several groups ( Hartfuss et al., 2001, Parnavelas et al., 1991 and Pinto et al., 2008). In addition, the discovery of the short neural precursor cell (SNP), which Alisertib order is located in the neocortical VZ and divides at the VZ to produce neurons, demonstrates that diversity Tryptophan synthase of the dividing cell population in the VZ is important for proper neocortical growth, even in rodents ( Gal et al., 2006 and Stancik et al., 2010). The cohabitation of the rodent VZ by RGCs and SNPs closely resembles the arrangement of GFAP+ and GFAP− cells in the primate VZ. Unlike RGCs, the SNPs do not contact the pial surface and are molecularly distinct as they express the tubulin alpha-1 DNA promoter but not the Glast promoter expressed by RGCs. Despite the power of the techniques used to highlight this newfound cell diversity, many of these cell types can be missed or misclassified, even when using modern methods, if they are

not bolstered by more time-consuming studies at higher levels of resolution or by using more elemental identifiers, such as gene expression. For example, while the cell division of multiple types of dividing precursors in the VZ has been monitored with time-lapse imaging, the cells with even substantial differences in morphology can be missed or misclassified if they are not reconstructed using classical methods with higher resolution, such as electron microscopy. In part to provide better resolution of cell type, recent studies have begun to use molecular analyses to highlight cell diversity. For example, SNPs and RGCs have been further differentiated by their use of the Notch signaling pathway; RGCs contain activated Notch while SNPs do not (Mizutani et al., 2007).